Open views naming the retired Snow style on Normal

createView threw on style 'snow', so an embed host or a
show_in_gods_eye_view call holding a view from before Snow was retired
was refused outright, camera and layers included. viewFromParams read
style=snow as the recipient's own style, while the app opened the same
link on Normal.

Both now read a retired style as Normal; truly unknown names still
throw. The retired list moves to a browser-free module shared by the
view API, the share codec and visual settings.

src/view/index.test.mjs

@@ -127,6 +127,14 @@ test('annotations travel in the link, keeping only what the app draws', async ()
   assert.equal(viewToParams(many).has('an'), false);
 });
 
+test('a view naming the retired Snow style opens on Normal', () => {
+  const camera = { lat: 1, lon: 2 };
+  assert.equal(createView({ camera, style: 'snow' }).style, 'normal');
+  const view = viewFromParams(new URLSearchParams('lat=1&lon=2&style=snow'));
+  assert.equal(view.style, 'normal');
+  assert.equal(viewToParams(view).get('style'), 'normal');
+});
+
 test('inherited and unknown style keys do not corrupt a restored view', () => {
   for (const style of [
     'constructor',